A hard disc drive, one of the magnetic storage devices in a computer, shows remarkable technical advances in achieving high-speed, high density, mass storage and the like. Its magnetic head for reading/writing is required to read/write on the surface of a magnetic disc rotating at a high speed, without a contact therewith but maintaining a small gap of a submicron order.
There can be mentioned a suspension board with a circuit, as a component for elastically pushing a magnetic head toward a magnetic disc surface rotating at a high speed, while resisting the airflow generated in the small gap, thereby to maintain a small gap between a surface of the magnetic disc and the magnetic head.
In a suspension board with a circuit, an elastic metal such as a stainless steel foil and the like is used as a material of the board, wherein one embodiment of the shape of the whole parts is, as shown in FIG. 1 of JP-A-10-12983 (Patent Reference 1), a kind of a band-like flat spring having a magnetic head mounting area and a circuit pattern.
A base end side of a suspension board with a circuit is fixed to an arm member extending from a device body of a hard disk driver and a magnetic head is mounted on a tip side (free end side), and the suspension board has a configuration wherein the board elastically supports the magnetic head on the tip side like a cantilever.
FIG. 9 is a schematic view of an enlarged tip part alone of a conventional suspension board with a circuit, and shows the configuration of the circuit and connections. A protective film covering the circuit, and so on have been omitted.
As shown in FIG. 9, the tip part of a metal board 100 has an area 130 to mount a magnetic head thereon, and a through-hole 140 is formed to surround therearound, whereby the area 130 is supported like a cantilever on the tip side alone at the center of the tip part of the metal board 100.
Furthermore, a conductive layer (circuit pattern shown with extra-thick line) 120 to transmit power, signal and the like is formed from the base side (leftward side of Figure, not shown) of the board to the terminal of the magnetic head on the metal board, via an insulating layer 110. Said circuit pattern 120 has a pattern end 121 to be a connection terminal (or terminal pad, electrode pad) is formed to connect a terminal of the magnetic head.
While various bonding methods have been proposed to connect the terminal of a magnetic head and an end of a pattern, techniques to connect them using a solder has been adopted in recent years so that even if the attached magnetic head is defective, only the magnetic head can be replaced easily without discarding the whole assembly.
Particularly, as a method for dealing with small terminals of magnetic heads and narrow-pitched arrangement thereof, connecting methods using a solder ball can be mentioned. As shown in FIG. 10(a), this connecting method comprises first arranging a terminal H11 of a magnetic head H10 and a pattern end (terminal pad for connection) 121 of a circuit closely to each other forming a right angle, and supplying a solder ball 150 in contact with both terminal surfaces. Then, a laser beam is irradiated on the ball to melt it as shown in FIG. 10(b) to establish a connection.
JP-A-10-79105 (Patent Reference 2) and JP-A-2002-50018 (Patent Reference 3) describe in detail connection methods using a solder ball, a supply device (solder ball supply element) of a solder ball and the like.
In contrast to the above-mentioned connecting method using a solder ball, the present applicant has focused attention on a fact that positional dispersion of the solder ball arranged on a pattern end is not preferable for laser beam irradiation and afforded a structure capable of reducing the dispersion to the upper surface of the pattern end (JP-A-2006-120288 (Patent Reference 4)). The invention of the Patent Reference 4, as shown in FIG. 4 of the reference, a stepped-part is provided on a surface of the pattern end for limiting the position of the solder ball and limiting a backward displacement of the solder ball, and as shown in FIG. 7 of the reference, two ridge-shaped protrusions are further formed and a solder ball is arranged between them. By the two ridge-shaped protrusions, displacement of the solder ball in a lateral direction (transversely) is suppressed, which improves a hit probability of the laser beam.
However, the present inventors have studied the above-mentioned structure of the Patent Reference 4 in detail, and found that as a circuit pattern or pattern end becomes more microfine, the space between two ridge-shaped protrusions is narrowed, and in some cases, the supplied solder ball rolls away and is scattered from the position where the solder ball should be held.
An object of the present invention is to provide a structure to a suspension board with a circuit, wherein a solder ball supplied during laser irradiation can stay stably at a given position and will not be lost easily.